1. Field of the Invention
The following description relates to apparatuses to detect a short in an LED array and an LED driving apparatus using the same, and more particularly, to a detecting circuit to accurately detect a short in an LED array and an LED driving apparatus using the same.
2. Description of the Related Art
A liquid crystal display (LCD) is widely used because it is thin and light in weight, and has a lower need for driving voltage and power consumption when compared to other displays. However, because the LCD is non-light emitting device that does not emit light itself, the LCD requires a separate backlight to supply light onto a LCD display panel.
Cold cathode fluorescent lamp (CCFL) and light emitting diode (LED) are generally used as the backlight source for the LCD. However, because the CCFL uses mercury, using CCFL causes environmental contamination. In addition, the CCFL has further shortcomings such as slow responsiveness, low color representation, and inadequacy to be used for LCD panels due to being heavy in weight and large dimensions compared to the widely used LCD panels.
In contrast, because the LED does not use environmentally-detrimental substances, the LED is environmentally friendly, and is drivable by impulse. Further, the LED provides good color representation and freedom to change brightness, color temperature, or the like as a user may wish by adjusting luminosity of red, green and blue LEDs. The LED is also appropriate for LCD panels in terms of being light in weight, thin, short, and small product. For the above-mentioned reasons, the LEDs are widely used as the backlight source for LCD panel, or the like.
For a LCD backlight employing LEDs, in order to implement an LED array using a plurality of LEDs connected in series, a driving circuit and a DC-DC converter are needed. The driving circuit provides a constant current to the LED, and the DC-DC converter adjusts electricity to the LED.
The LED array often has a problem of being short after operating for a long time or due to impact. Accordingly, a protection circuit is necessary to detect the short of the LED array.
For example, a protection circuit could be provided to measure feedback voltage (VFB) of the LED array to detect the short of the LED array. However, the settling time of the constant current source, which is irrespective of the short of the LED array, or abnormal feedback voltage (VFB) due to peak current of the constant current could be detected as the short in the LED array.
FIG. 11 is a waveform of a driving voltage and a feedback voltage according to a conventional LED driving apparatus.
In FIG. 11(a), the driving voltage higher than a target voltage is applied to the LED array to turn on all the LED arrays during initial LED driving. In FIG. 11(b), high driving voltage is sometimes temporarily applied to the LED array during LED driving. However, the feedback voltage increases as high driving voltage is applied to the LED array. As a result, a protection circuit in the conventional LED driving apparatus erroneously detects such temporary increase of feedback voltage as a short in the LED array.